The present invention relates to a diagnosing apparatus and method for RAM used in a control microcomputer for controlling a variety of electronic controlled devices such as in a vehicular engine.
In a control apparatus for a vehicular engine, there has been conducted hitherto diagnosis such as of ROM and RAM by a CPU of a control microcomputer, in addition to self-diagnosis of the CPU (refer to Japanese Unexamined Patent Publication No. 64-19401).
In RAM diagnosis, there is conducted read-write check on a diagnosis object RAM by for example 4 bytes at each of predetermined diagnosis timing, and when a failure (NG) is detected, the diagnosis result is written, as a flag, into a predetermined address of the RAM itself.
Further, the flag indicating the diagnosis result is read out, and when the flag indicates existence of failure, there is conducted a fail-safe processing such as turning OFF of power source of the control object equipment.
However, in such a conventional RAM diagnosing apparatus, the diagnosis result is written, as a flag, into the RAM as a diagnosis object. As such, it has been a problem that the processing can be hardly shifted to the fail-safe processing even when a failure has been detected by the RAM diagnosis, if the flag itself for the diagnosis result fails.
In view of the conventional problem as described above, it is an object of the present invention to enable reliable shift to a fail-safe processing upon detection of failure by RAM diagnosis.
To this end, with the present invention, there is provided a diagnosing apparatus for a RAM comprising: a RAM diagnosing device for diagnosing a RAM used in a microcomputer; a diagnosis result storing device for doubly storing the diagnosis result of the RAM diagnosing device, as flags, into mutually different two addresses of the RAM; and a fail-safe processing device for conducting a fail-safe processing based on the doubly stored diagnosis result flags when at least one of the flags indicates existence of failure.
According to this constitution, the diagnosis result of the RAM diagnosis is doubly held and the processing is shifted to the fail-safe processing based on OR of the doubly held diagnosis result, thereby obtaining such an effect that the shift to the fail-safe processing is reliably conducted when a failure is detected by the RAM diagnosis.
In the above, the bit allocation of the doubly stored flags may be separately established, so as to cope with bit-line failure. To this end, the diagnosis result storing device may doubly store the diagnosis result into the mutually different two addresses and at mutually different bit positions of the RAM.
Further, to cope with failure in word lines, the address assignments of the doubly stored flags are offset from each other by a predetermined address interval. To this end, the diagnosis result storing device may doubly store the diagnosis result into two addresses of the RAM, which are different from each other and which have an address interval therebetween other than an address interval of word lines.
Moreover, with the present invention, there is provided a diagnosing apparatus for a RAM comprising: a RAM diagnosing device for diagnosing a RAM used in a microcomputer; a diagnosis result storing device for storing the diagnosis result of the RAM diagnosing device, as a flag, into a predetermined register; and a fail-safe processing device for conducting a fail-safe processing based on the diagnosis result flag stored in the register when the flag indicates existence of failure.
According to this constitution, the diagnosis result of the RAM diagnosis is stored in the register of the CPU side and the processing is shifted directly to the fail-safe processing from the register, thereby obtaining such an effect that the shift to the fail-safe processing is reliably conducted when a failure is detected by the RAM diagnosis.
In the above, the RAM diagnosing device may diagnose the RAM in a read-write manner.
Further, concretely, the fail-safe processing device may turn OFF power source of control object equipment of the microcomputer.
Characteristic features of the present invention and the resultant operation and effects will become apparent from the embodiments described hereunder.